Not an expert in this domain but I'll cover the basics: ecurities are a euphemism for stocks and similar. Banks have been loaning out the money you deposit since the beginning of time; it's how they make money. They don't keep all the cash that people have deposited on hand, which is why a "run on the bank" was problematic in the past. They basically keep enough cash around ("reserves") so that the average withdrawals don't get them into trouble. And yes, you are certainly not choosing the investments that the bank makes with your money. And they're not "your" investments: the bank pays you a small fee (3% in this case) and then takes risks with your money to make a higher return and keep the difference.
I'd recommend reading up on the Federal Reserve (The Creature from Jekyll Island), the modern financial system (any of Michael Lewis's books, especially Boomerang and The Big Short), and maybe the first global banking families (The Medicis: Power, Money, and Ambition in the Italian Renaissance). We're talking about the power structure of the world here and it's good to be informed on the main points.
So what does that mean here? Are you saying that the part of your money that the bank uses to invest, is not insured? If so, then what does the insurance for the remainder even mean? Money that the bank doesn't touch doesn't need to be insured, because it's always there. The whole point of such an insurance is to reimburse you in case the bank loses your money due to their bad investment. If that's not covered but only the part that they never touch, then the whole insurance becomes meaningless.
I still suspect that the securities mentioned are your own securities rather than the bank's, which makes it totally sensible that they're not covered by the insurance.
My understanding is that yes, you're not covered if the bank suffers losses and passes them on to you. The entire industry is one giant moral hazard due to complete lack of skin in the game on the part of the banks. They don't own the money and aren't responsible for catastrophic losses (see the '08 and previous bailouts), but they control it and keep the upside. You're right, that insurance sounds like garbage, but I haven't bothered to dig into the details. Caveat emptor!
"Own nothing, but control everything." -John D. Rockefeller
edit: good note from /u/snowwrestler below:
> > It's not the cash/securities that Robinhood holds as part of their business, it's the one they hold for you. You may well choose to hold 100% cash or 100% securities.
> If I'm holding 100% securities, a) SIPC offers me no protection from losses, b) I better be making more than 3% return, and c) I would not call that situation "a checking account."
I think the loss case they're protecting you for is more
"I bought 100 shares of Acmecorp, then Robinhood shuttered their doors and said they sold the shares to fund their yacht."
The SIPC's job there is to reimburse you for 100 shares of Acmecorp as of now; they're not going to let investors cherry-pick and say "but they mishandled the account during the one day it was at its peak and I want that price!"
I'd recommend reading up on the Federal Reserve (The Creature from Jekyll Island), the modern financial system (any of Michael Lewis's books, especially Boomerang and The Big Short), and maybe the first global banking families (The Medicis: Power, Money, and Ambition in the Italian Renaissance). We're talking about the power structure of the world here and it's good to be informed on the main points.